The broad objective of this research is to quantitatively define visual and vestibular mechanisms which control eye movements. More specifically, the experiments of this proposal aim to (a) define the dynamic characteristics of the otolith-ocular reflexes and otolith-optokinetic interactions, and (b) formulate a mathematical model to describe the neural mechanisms controlling vertical eye movements. Alert cats and human subjects will be subjected to natural stimulation: rotation of the subject in the dark (vestibular alone) or in the light (vestibular and visual) or rotation of the subject's visual surround (vision alone). Dynamic otolith stimulation will be by rotating subjects who are positioned off the axis of rotation. For the animal experiments, some cats will have their semicircular canals plugged so that otolith function can be assessed. Some human subjects will have a unilateral vestibular deficit so that interactions due to different vestibular inputs from the two ears can be studied. The results of this work should further our understanding of the basic physiology of the vestibular and oculomotor systems and may suggest some protocols to clinically evaluate otolith function.